1. Field of the Invention
The present invention relates to a transmitting apparatus using a multiple lambda source in a Wavelength Division multiplexing (WDM) network. More particularly, the present invention relates to a transmitting apparatus using a multiple lambda source in a WDM network. The multiple lambda source has an improved structure enhancing the performance of the transmitting apparatus, and has the potential of unify standards of subsystems.
2. Description of the Related Art
In the field of very high-speed optical communication, Wavelength Division multiplexing (WDM) that utilizes a plurality of optical channels is employed in transmitting large quantities of data through a single optical fiber. It is expected that in future, optical communication networks will evolve from the current linear or ring networks in which data are transmitted through fixed lines into an all-optical transmission network in which optical paths can be changed according to necessities so as to dynamically reconstruct the network. Particularly, it is expected that mesh type networks, which are based on Optical Cross-Connectors (OXCs) capable of restructuring a circuit at each node, will become backbone networks.
Optical Cross-Connectors (OXCs) may be implemented by an electrical method or an optical method. In the electrical method, an inputted optical signal is converted into an electrical signal by means of a light/electricity conversion, and the electrical signal is again converted into the optical signal after switching. In the optical method, a wavelength multiplexed optical signal inputted from an input link is demultiplexed and then switched according to the wavelength by a space switch.
Typical OXCs according to the conventional optical method may be classified into OXCs employing a transmitting apparatus using a wavelength converter and OXCs employing a transmitting apparatus using a tunable wavelength light source. The present invention pays attention to only a transmitting apparatus of an OXC other than the other portion of the OXC which receive an electrical signal. Therefore, the following description will center on the transmitting apparatus.
FIG. 1 shows a conventional transmitting apparatus utilizing a wavelength converter in a WDM network of the prior art.
The transmitting apparatus shown in FIG. 1 includes n direct modulated laser diodes 11-1 through 11-n, an optical space switch 12 for performing a line distribution by changing the state of connection of optical signals from the n direct modulated laser diodes 11-1 through 11-n, n wavelength converters 13-1 through 13-n for changing the optical signals having been line-distributed by the optical space switch 12 into signals having wavelengths that may be used by a multiplexer 15, n laser diodes 14-1 through 14-n for providing tuned wavelengths that are needed for wavelength conversion in the n wavelength converters 13-1 through 13-n, and a multiplexer 15 for multiplexing the transport signal channels which are inputted from the n wavelength converters 13-1 through 13-n.
The transmitting apparatus described above generates optical signals using the n direct modulated laser diodes 11-1 through 11-n. The optical signals are provided to destined channel ports of the multiplexer 15 by the optical space switch 12. In this case, the n wavelength converters 13-1 through 13-n are used in converting the wavelengths of the n direct modulated laser diodes 11-1 through 11-n into wavelengths matching the ports of the multiplexer 15 in order to prevent a wavelength contention.
However, because this transmitting apparatus needs a wavelength converter for each channel and a laser diode for providing tuned wavelengths required in wavelength conversion for the operation of each wavelength converter, such a transmitting apparatus is very expensive. Further, because too many components are necessary for constructing this transmitting apparatus, the design is very complicated.
FIG. 2 shows a transmitting apparatus utilizing tunable laser sources for use in a WDM network of the prior art.
The transmitting apparatus depicted in FIG. 2 includes n tunable laser sources 21-1 through 21-n, n modulators 22-1 through 22-n for modulating optical signals from the n tunable laser sources 21-1 through 21-n, an optical space switch 23 for performing a line distribution by changing the state of connection of modulated signals from the n modulators 22-1 through 22-n, and a multiplexer 24 for multiplexing transmitting signal channels which are line distributed by the optical space switch 23.
In this transmitting apparatus, because the tunable laser sources receive information about the state of the optical space switch and convert the wavelengths to wavelengths matching the ports of the multiplexer, such a wavelength converter as depicted in FIG. 1 is not required.
However, the tunable laser source has several drawbacks, including the fact that it is very expensive and has a relatively low response speed. Further, the delay time of the tunable laser source is added to the switching time, thereby further increasing the response time of the tunable laser source. Accordingly, the tunable laser source is not suitable for a transmitting part of an optical cross-connector which requires a high speed of conversion.